Quantitative assessment of histological regression in peritoneal carcinomatosis (QARP) as a modified scoring system after pressurized intraperitoneal aerosol chemotherapy – a pilot study

Introduction/Aim: Peritoneal carcinomatosis is a leading cause of death in gastrointestinal cancer patients. Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is a newer treatment concept in these patients. During PIPAC, a chemotherapeutic drug is applied to the abdominal cavity as an aerosol under pressure to directly treat peritoneal disease. To date, treatment response can be assessed macroscopically by determining the Peritoneal Cancer Index (PCI) and/or microscopically by using the Peritoneal Regression Grading Score (PRGS). Here, we present a new modified scoring system to quantify treatment response after PIPAC: Quantitative Assessment of histological Regression in Peritoneal carcinomatosis (QARP).

Material and methods: Peritoneal biopsies were obtained from 27 patients with gastrointestinal cancers and peritoneal metastases who had each undergone 2-6 PIPAC procedures, and processed in a standardized fashion. After each PIPAC, biopsies were scored according to our new 5-tiered grading system, QARP: grade 0: no residual tumor cells with regressive changes present; grade 1: 1-25% viable tumor cells per tumor focus with regressive changes present; grade 2: 26-50% viable tumor cells per tumor focus with regressive changes present; grade 3: 51-75% viable tumor cells per tumor focus with few regressive changes; grade 4: more than 75% viable tumor cells per tumor focus with minimal or no regressive changes.

Results: Median age was 62 years. Cancer origin was esophagogastric in 8 patients (30%), colorectal in 10 (37%), pancreatic in 5 (19%), biliary in 3 (11%), and appendiceal in 2 (7%). Colorectal cancer patients received oxaliplatin-based PIPAC. All other patients received doxorubicin/cisplatin. Improvement in QARP score or stable low QARP scores (0 or 1) were seen in 14 patients (“QARP responders”), stable high QARP (4) or worsening scores over time were detected in 13 patients (“QARP non-responders”). Higher QARP scores significantly correlated with higher PCI (r=0.32; p=0.007). QARP responders showed a significant survival advantage at 6 months, but no difference over the entire study period.

Conclusion: Here, we present our new scoring system combining elements of the PRGS with a semiquantitative assessment of tumor cells versus regressive changes. Further studies are necessary to ascertain the reproducibility and prognostic significance of QARP to better identify patients who benefit the most from intraperitoneal chemotherapy application.

Publication History

Article published online:
26 September 2024